Face ID permits a single user to register their face, as opposed to Touch ID which supports up to five different fingerprints. Apple’s chief of software engineering explains why.

In an alleged response to an email inquiry from a customer, shared on Reddit, Federighi explains that Touch ID was never intended for multiple users anyway.

Here’s Federighi’s response in full:

Currently, we’re focusing Face ID on single-user authentication. Even Touch ID’s multi-finger support was really intended to enable a single iPhone owner to unlock the device with a finger and thumb on both hands, not to enable multi-user authentication.

Apple’s Senior Vice President of Software Engineering wrapped up by noting that Apple will keep feedback like that in mind “as we consider our plans to evolve Face ID in the future.”

MacRumors notes that the email is probably authentic given that the Reddit user who shared it has a good reputation and history on the website. “However, we are still waiting to receive full headers of the email to verify its origins,” notes the publication.

It’s thought that Face ID’s single-user design stems from it being a brand new biometric feature that Apple wants to get right before introducing multi-face support. Another speculation has it that matching the user’s face against multiple registered faces would slow down response time noticeably due to the sheer amount of processing power required for 3D facial recognition.

Overall, I’m not concerned because I’m sure Apple will iterate Face ID so I’m expecting it to support multiple faces in the future. That said, however, I can see how this is annoying those who may want to share their device easily with trusted family members or friends.